This proposal involves the molecular genetic analysis of a set of interacting regulators of gene expression. The first of these is the bacteriophage P22 antirepressor, a novel regulatory protein which works by inactivating other regulatory proteins (phage repressors). Synthesis of antipressor is in turn under negative control by 2 regulatory mechanisms, the P22 arc and mnt gene products. A combination of genetic and biochemical approaches can be used to analyze the mechanism of action and specificity of P22 antirepressor. The inactivation of phage lambda repressor by antirepressor can be studied in a purified in vitro system; this work is likely to demonstrate a new principle of regulation--that of control by non-covalent interaction between regulatory proteins. Furthermore, it should reveal the nature of the determinants that allow the antirepressor and repressor proteins specifically to recognize each other. The arc and mnt regulators have been defined genetically but their mechanisms of action are unknown. I plan to determine how the mnt and arc functions regulate antirepressor synthesis; the first question to answer is whether expression of the antirepressor gene (ant) is controlled at the transcriptional or post-transcriptional level. To answer this question, the effect of the arc and mnt functions on the amount and form of ant gene transcripts can be studied in vivo. Finally, I plan to identify the mnt and arc proteins and determine whether the mnt, arc, and ant genes are all expressed from separate promoters or whether any combinations of them are coordinately expressed.